1. Field of the Invention
This invention relates to flow control apparatus and, in particular, to flow control apparatus utilizing a double valve arrangement to control two fluid streams.
2. Description of the Prior Art
In flow control apparatus a frequently encountered problem is the maintenance of a substantially leak-free engagement between a valve plug member and its associated valve seat. It was early appreciated that the provision of a dual valve plug arrangement enhanced the ability of the apparatus to maintain substantially leak-free operation for periods of time in excess of the normal single valve plug-seat arrangement. U.S. Pat. No. 1,256,759 (Wilson) typifies a tandum connection of first and second valve members. U.S. Pat. No. 1,206,319 (Flanders) discloses a two valve motive fluid controller for turbine apparatus in which both valves are operatively associated to an externally pivoted actuator.
Other valve apparatus of the prior art, such as U.S. Pat. Nos. 1,593,260 (Hittenmeyer), 2,403,029 (Smith), and 2,830,620 (Shuptrine) disclose double valve constructions in which the first valve is concentrically disposed relative to the second valve and operable such that opening of the first valve is delayed for a predetermined time after the opening of the second valve. U.S. Pat. No. 1,956,082 (Schneible) relates to a double valve arrangement disposed on a common shaft. U.S. Pat. No. 1,540,954 (Rockwell) disposes a two valve plug arrangement in which a first valve concentrically surrounds the shaft of the second, plug-type valve and wherein movement of a common shaft opens the plug-type valve before openings provided in the concentric valve member register with an outer, stationary partition to permit fluid passage from the valve inlet to the outlet.
Other valve arrangements are known in the art which utilize a sliding plate to separate and prevent fluid communication between a valve inlet and outlet. For example, U.S. Pat. No. 3,701,359 (Worley) discloses an insulated slide valve wherein the sliding valve plate moves away from sealed contact with a large outlet pipe before the valve plate moves away from seated engagement with a smaller diameter inlet pipe. Once the plate is opened, however, a discontinuity in the flow passage occurs, thus leaving open the possibility that foreign matter entrained in the fluid flow may become lodged in the recess provided for seating of the valve plate, thus negating the capability of the valve to fully seat in the closed position. Also, wearing effects occur across the inlet and outlet edges of the conduits as the plate is withdrawn in the face of a pressurized fluid.
U.S. Pat. No. 3,575,377 (Carlton) illustrates a closure seal for a gate valve in which pressurized fluid from each side of the valve plate is utilized to maintain seal integrity between the valve plate and the valve casing. U.S. Pat. No. 3,926,408 (Vogeli) discloses a gate valve for controlling fluid flow.
In the field of flow control of two fluid streams by a single operator or actuator, such as control of hot and cold water into a basin, U.S. Pat. No. 3,460,571 (Moen) and U.S. Pat. No. 3,620,254 (Mongerson, et al.) disclose handle valve arrangements. Also, valves known in the art as the the Delta valve, manufactured by Delta Faucet Company, of Greensburg, Indiana, are available. Such valves utilize a rotatable ball member with flow passages therethrough which rotates about an axis thereof to align with separate fluid flow conduits to conduct fluid from those conduits to a mixing region downstream of the ball. Also available in the prior art is a valve manufactured by Peerless Valve Company, which utilizes a cylindrical member as the valve element. The cylinder is provided with a passage having one terminus in the planar end of the cylinder and a second terminus in the curved surface of the cylinder. The cylindrical member is rotated about an axis therethrough to bring the second terminus of the passage into registration with an outlet orifice provided in the valve housing.
However, as appreciated by those with skill in the art, the machining of a precise spherical or cylindrical members, as the ball and its seating chamber or the cylinder and its associated seating chamber, requires careful workmanship and specialized machinery in order to avoid leakage around machined imperfections when the ball or cylinder is placed within the valve and to avoid early failure when operated due to surface imperfections of the curved members.
It is therefore of advantage to provide a valve for control of two fluid streams which utilizes a configuration of a flat plate or plates as the valve element. It is advantageous to provide a double-valve arrangement for control of two fluids which provides substantially leak-free operation for extended period of time yet utilizes the sliding type valve plug as the only moveable element. It is of further advantage to provide a valve of such construction so that the outlet orifice is open prior to the opening of the inlet orifice. It is of further advantage to provide a valve plug having first and second partition, each having an orifice therein, each of which cooperate to define a valve plate chamber in which a rectilinearly or rotationally slidable valve plate as disposed. It is advantageous to provide a valve so that sliding of the valve plate rectilinearly within or angularly into and out of the valve plate chamber places a passage disposed in the valve plate into communication with the outlet orifice prior to registration with the inlet orifice. It is of further advantage to provide a valve wherein the inlet and outlet orifices register to provide an enclosed flow passage to avoid accumulation of foreign matter in any open recesses within the valve.
It is also advantageous to provide a double valve arrangement utilizing a first, upstream, valve of a sliding type and a second, downstream, valve of the plug type and to provide a common, externally-pivoted actuator such that movement of the actuator opens the downstream valve prior to the unseating of the upstream valve.